The present invention relates to covers disposed over openings extending downward through roadways, and in particular, to mats which occupy cavities bounded by the tops of the covers and the roadway disposed about the covers.
Openings are formed in roadways to provide access to things disposed beneath the roadways, including, for example, water and sewage lines. One commonly known opening is a manhole, which is typically defined by a frame set in the roadway, and sealed by a manhole cover resting on top of the frame. One problem associated with manhole covers is that they do not always remain flush with the surrounding road surface. For example, roadways often buckle or heave in response to temperature changes associated with the different seasons of the year. Also, when roadways are resurfaced, additional material is added to the road surface disposed about the manhole frame. In either of these cases, the road surface increases in elevation relative to the top of the manhole cover, leaving a cavity or depression in the surface of the road.
One proposed solution to the foregoing problem is to fill the depression with asphalt. However, this approach suffers shortcomings, including the inconvenience of applying the asphalt; the inconvenience of removing the covering when access to the opening is desired; the durability of the small, isolated patch of asphalt; and/or the inconvenience of removing the asphalt in the event that the road surface returns to an earlier, relatively lower level.
Another proposed solution to the foregoing problem is to add a ring on top of the manhole frame (beneath the cover) to raise the height of the manhole cover. However, this approach suffers shortcomings, as well, including the inconvenience of installing the ring; the unsuitability of the rings for adjustments less than one and one-half inches and/or for adjustments in increments as little as one-quarter of an inch; and the inconvenience of removing the ring in the event that the road surface returns to an earlier, relatively lower level.
In other words, a need remains for a convenient and effective system which compensates for elevational changes between a manhole cover and the surrounding road surface.
One aspect of the present invention is to mount a mat or surface elevation riser on top of an access cover for purposes of eliminating an elevational discrepancy between the surface of the cover and the surface of the surrounding roadway. This inventive solution to the problem discussed above in the Background of the Invention is not as simple as it may first seem to those unfamiliar with the installation considerations and environmental conditions associated with access covers, such as manhole covers. For example, many manhole covers are regularly traversed by vehicles of various weights, traveling in various directions, and/or at various speeds. Also, many different installation parameters may vary from one setting to the next. Moreover, work on the covers typically involves the diversion of traffic, thereby placing a premium on rapid project completion.
A preferred embodiment of the present invention includes a mat which is bolted to an underlying cover. Relatively thin, flat heads are provided at one end of the bolts, and lock nuts are threaded onto opposite ends of the bolts in such a manner that the heads do not protrude above the surface of the mat. The threaded ends of the bolts, as well as the lock nuts, are disposed beneath the cover and out of harm""s way.
The preferred embodiment mat is made of recycled rubber, 67 durometer, and may be as little as one-half inch thick. The mat may be configured to provide access to a lift hole or other special opening in the cover. The mat also may be configured to overlie any such openings and/or the seam between the cover and adjacent structure, thereby reducing passage of water and/or debris through the opening. Assuming a substitute cover is available, the mat may be installed and/or removed off-site, thereby reducing disruption of traffic. Additional aspects and advantages of the present invention will become apparent from the more detailed description that follows.